(1) Field
This invention relates to a device for locating a locally deforming contact on a deformable touch-sensitive surface of an object. It also relates to a method implemented by this device.
(2) Description of the Related Art
There are many objects that have a touch-sensitive surface, including mobile phones and other portable personal digital assistance devices. Their touch-sensitive interface is usually a flat rectangular screen with which a user can interact using a stylus or a finger. Note, however, that the invention relates more generally to any type of object having a deformable touch-sensitive surface that is not necessarily flat or rectangular in shape. It therefore advantageously applies to communicating objects with a touch-sensitive and intuitive man-machine interface, such as robots, having a three-dimensional deformable shell attached to a rigid support by a limited number of attachment points.
By a “deformable” shell or touch-sensitive surface, this means a two-dimensional or three-dimensional surface, capable of changing shape in the sense of the static and dynamic elasticity of its materials when it is subjected to static or dynamic stress, such as a touch, a contact force, a mechanical impulse, or even a shock, and able to exhibit resonant vibrations when it is excited by elastic mechanical waves, such as impulses, so as to deform by bending, even on a submillimetric scale that is imperceptible to the naked eye. Plastic, glass, or metal shells are suitable.
All known objects with a touch-sensitive surface have a device for locating touches or impacts using one or more detection techniques. A strong trend to reduce the manufacturing cost and to reduce congestion aims to adopt only the simplest technologies that use a limited number of sensors. The invention thus relates more specifically to a locating device that implements a technology to detect the propagation of elastic mechanical waves on a touch-sensitive surface, particularly through the use of detectors, such as piezoelectric transducers.
A first solution is disclosed in French patent applications published under numbers FR 2 725 513, FR 2 787 608, and FR 2 811 107. It is based on measuring a time interval for transferring a wave packet to multiple piezoelectric detectors and on the deterministic calculation, using a pre-established mathematical formula, of the position of a source that transmits said wave packet. This wave packet is more specifically transmitted by an acoustic source coming into contact with the touch-sensitive surface. Generally, it is then possible to locate an impact of a finger or stylus, since that is then the issuer of an impulse. But with this technology, it is not possible to detect the persistence of a touch after impact or the movement of the acoustic source on the touch-sensitive surface, except to plan that the acoustic source regularly transmits wave packets. One is then limited to applications that use a stylus that repeatedly transmits wave packets. In addition, this technology is well suited to touch-sensitive surfaces presented in the form of isotropic flat plates, but poorly suited to any three-dimensional shells that do not allow for a deterministic calculation of the position of the acoustic source using a pre-established mathematical formula. Finally, this technology does not detect a static stress or the force of a touch (stroke, inimical interaction, etc.).
A second solution is disclosed in the French patent application published under the number FR 2 841 022. It is based on a recognition of the position of an impact by learning. The implemented method operates a cross-correlation between at least one acoustic signal measured from the detection of an acoustic wave generated by an impact on the touch-sensitive surface of the object and a reference set, called a “signatures set”, comprised of prerecorded acoustic impulse responses, each being relative to a predefined position that one wants to associate to a function and recognize when an impact occurs at that position. Here again, it is possible to locate an impact, but not the persistence of a touch after the impact, the movement of a finger or of a stylus on the touch-sensitive surface, a static stress, or the force of a touch. However, this solution is well suited for any three-dimensional shells, even those having a complex shape.
To be able to more effectively measure any touch, specifically its persistence, whether it is a static touch or a movement, another solution consists of measuring the disruption of a touch on the propagation of elastic mechanical waves regularly transmitted in the touch-sensitive surface independent of this touch.
The invention relates to this type of solution. It thus applies to a device for locating a locally deforming contact on a deformable touch-sensitive surface of an object, comprising:                at least one transmitting transducer designed to transmit elastic mechanical waves propagating in the deformable touch-sensitive surface of the object,        at least one receiving transducer designed to capture elastic mechanical waves propagating in the deformable touch-sensitive surface of the object, and        a central processing unit, connected to the transmitting and receiving transducers and programmed to analyze a signal captured by the receiving transducer and to deduce from it the presence or absence of a touch.        
Such a device is described in the international patent applications published under the number WO 2008/142345. It more specifically provides for a reliable location of a touch by propagating waves having multiple frequency components corresponding to natural vibrational frequencies of the object. The propagation of these waves over a period of time in the touch-sensitive surface can identify patterns of vibration at different wavelengths, including resonant traces of bending modes. These have the characteristic of being more highly disrupted than resonant traces of modes with vibrations on the plane of the touch-sensitive surface of the object, so that the cushioning or absorption generated by a finger in contact with the touch-sensitive surface, even if it is thick, varies measurably from one natural mode to another and from one contact position to the other. It is then possible to locate a touch by a learning method, once a sufficient number of resonant traces are identified on the surface of the object.
This method offers the advantage of requiring only a small number of transmitting and/or receiving transducers, and it can operate on three-dimensional shells of any shape with a measurement rate of up to several dozen locations per second. However, to function effectively, this device requires a touch having a sufficient contact surface with the touch-sensitive surface in order to achieve detectable absorption. It is therefore poorly suited for detecting near-pinpoint touches, such as those caused by the tip of a stylus. It is also well suited for thin shells but poorly suited for thick shells.
It may therefore be desirable to provide a device for locating a locally deforming contact on a deformable touch-sensitive surface of an object that overcomes at least some of the problems and constraints mentioned above.